Exposure of domestic animals to Mayaro and Oropouche viruses in urban and peri-urban areas of West-Central Brazil

Oropouche and Mayaro viruses are enzootic arboviruses of public health concern throughout Latin America. Recent outbreaks of OROV in northern region and sporadic autochthonous cases in western region of Brazil, suggest a silent circulation of these neglected viruses. Aiming to investigate the exposure of different species of domestic animals to MAYV and OROV in urban and peri-urban areas of West-Central Brazil, we performed a cross-sectional serosurvey by plaque reduction neutralization test (PRNT). Our findings included neutralizing antibodies for both arboviruses in cattle, dogs and horses, suggesting eventual role of domestic animals in enzootic arbovirus surveillance in Brazil.


Introduction
Mayaro virus (MAYV, Togaviridae) and Orthobunyavirus oropoucheense (OROV, Peribunyaviridae) are mosquitoborne enzootic arboviruses involved in outbreaks of human febrile illness, mostly reported in northern South America, including the Amazon region in northern Brazil, and neighboring countries [1,2].Although most infections in humans are asymptomatic, symptomatic individuals mostly present mild acute febrile illness in a self-limiting clinical course.Few individuals will present intense and sometimes chronic arthralgia caused by Brazil have showed the exposure of domestic animals to several enzootic arboviruses, including MAYV and OROV, in addition to epidemic arboviruses such as Zika virus [12][13][14].Here, we aim to assess the presence of neutralizing antibodies (NAb) for MAYV and OROV by plaque reduction neutralization test (PRNT) in plasma samples of several species of domestic animals from urban and peri-urban areas of the states of Mato Grosso and Mato Grosso do Sul, West-Central Brazil.

The study
We performed a cross-sectional serosurvey and convenience sampling in domestic animals from 17 subsites in urban and peri-urban areas of Campo Grande, capital of the state of Mato Grosso do Sul (MS) and Cuiabá, capital of the state of Mato Grosso (MT), located in West-Central Brazil, between April 2017 and March 2018 (Fig. 1).Animal sampling was approved by the Animal Ethics Committees in compliance with the requirements of Brazilian Law 11,794/2008, decree 6899/2009.
The short viremia period associated with arbovirus infection may result in underreporting of exposed animals if only molecular tools are used for diagnosis [12].It is also worth mentioning that, in a previous study, MAYV and OROV RNA was not detected in these samples [11].Therefore, serosurveys for the detection of NAb are a reliable approach to confirm enzootic arbovirus exposure during surveillance programs.
Our findings suggest previous exposure of domestic animals to MAYV and OROV in Cuiaba and Campo Grande, populated cities located in the West-Central Brazil.Although the possibility of cross-reaction cannot be completely ruled out, evidences of MAYV and OROV infections in humans and vectors from the same area corroborate the results presented here [5,7,[13][14][15].Together, these findings reveal that MAYV and OROV have been circulating in populated areas of West-Central Brazil.Moreover, serum samples from humans and backyard chickens collected in 2019 in the hinterland of the state of Ceará, located in Northeast Brazil, showed hemagglutination-inhibiting antibodies to MAYV [16].OROV detection in human, vectors and animal samples in populated areas is a major concern.Molecular detection of OROV in the states of Bahia and Minas Gerais, touristic and densely populated areas in Brazil, reveals the potential for transmission and dissemination to other areas in the country and elsewhere [5,6].
Prediction models of risk areas and outbreak modeling indicate that different regions are favorable to the dispersion of OROV and MAYV throughout Brazil and other Latin American countries [1,10,17].These data associated to recent detection of MAYV and OROV outside Amazon in the absence of outbreaks suggests that the circulation of these viruses in Brazil may be underreported in non-enzootic regions.

Limitations
Limitations of our study included the limited species of alphaviruses and orthobunyaviruses used for the differential diagnosis by PRNT.Even though we only considered as OROV or MAYV-seropositive those samples with a titer greater than 20 and used a conservative threshold of 90% of neutralization, other related viruses may be circulating in our study sites.Sampling bias can be considered as a limitation, since the animals were sampled by convenience.

Conclusions
The findings presented here suggest that dogs, horses and cattle sampled in populated cities of West-Central Brazil have been exposed to MAYV and OROV.These results raise concern about the potential urbanization of MAYV and OROV in Brazil, and show that comprehensive data on the serological status of domestic animals' populations can be important for arboviruses' surveillance that ultimately may guide public policies.

Fig. 1
Fig. 1 Subsites used for sampling of domestic animals in the West-Central region of Brazil

Table 1
Domestic animals from urban areas of West-Central Brazil presenting NAb for MAYV and/or OROV in PRNT 90 assay